A conventional bipolar battery generally includes electrodes having a metallic substrate on which positive active material forms one surface and negative active material forms the opposite surface. The active materials are retained by various means on the metal conductive substrate which is nonconductive to electrolyte ions. The electrodes are arranged in parallel stacked relation to provide a multicell battery with electrolyte and separator plates providing an interface between adjacent electrodes. Conventional monopolar electrodes, used at the ends of the stack are electrically connected with the output terminals. While achieving respectable power densities, these conventional bipolar battery designs suffer substrate corrosion, seal and active material retention problems. For these reasons, bipolar versions of the standard lead acid battery have failed to gain commercial success.
Most bipolar efforts to date have used metallic substrates. Specifically, bipolar lead-acid systems have utilized lead and alloys of lead for this purpose. The use of lead alloys, such as antimony, gives strength to the substrate but causes increased corrosion and gassing. In addition to the problems of forming a liquid tight seal between the metallic substrate and adjacent nonconductive case (frame) materials, substrate corrosion, weight and strength factors have also been unacceptable. Furthermore, any attempt to reduce weight has lead to increased problems of strength and corrosion. Accordingly, a different approach must be used if acceptable weight and life are to be simultaneously achieved.
Alternate approaches have included substrates of a synthetic resin such as polystyrene incorporating therein metal or graphite powder (U.S. Pat. No. 3,202,545), a plastic frame of polyvinyl chloride with openings carrying a battery active paste mixed with nonductive fibers and short noncontacting lead fibers for strengthening the substrate (U.S. Pat. No. 3,466,193) a biplate having a layer of zinc and a polyisobutylene mixed with acetylene black and graphite particles for conductivity of the plate (U.S. Pat. No. 3,565,694), a substrate for a bipolar plate including polymeric material and vermicular expanded graphite (U.S. Pat. No. 3,573,122), a rigid polymer plastic frame having a grid entirely of lead filled with battery paste (U.S. Pat. No. 3,738,871), a plastic thin substrate having lead stripes on opposite faces, the lead stripes being interconnected through an opening in the substrate, and retained by plastic retention strips (U.S. Pat. No. 3,819,412) and a biplate having a substrate of thermoplastic material filled with finely divided vitreous carbon and a layer of lead antimony foil bonded to the substrate for adhering active materials (U.S. Pat. No. 4,098,967).
Such prior biplate constructions were characterized by the support of active material on the biplate substrate and various physical configurations for purposes of strengthening the biplate. Conventional metallic substrates presented seal and corrosion problems.